High efficiency module

ABSTRACT

A module ( 1 ) includes a first functional device ( 2 ) and a second functional device ( 3 ). The first functional device ( 2 ) includes a base electrode, an emitter electrode and a collector electrode. The second functional device ( 3 ) includes at least one electrode. The module ( 1 ) further includes a conductive frame ( 4 ). One of the base electrode, the emitter electrode, and the collector electrode of the first functional device ( 2 ) is directly connected to the frame ( 4 ). The electrode of the second functional device ( 3 ) is also directly connected to the frame ( 4 ). The frame ( 4 ) includes a portion serving as a terminal for external connection.

TECHNICAL FIELD

The present invention relates to a module with reduced wiring inductanceand resistance between mutually connected functional devices.

BACKGROUND ART

A synchronous rectification type DC-DC converter that includes a metaloxide semiconductor field effect transistor (MOSFET) in place of arectifying diode is known. FIG. 13 is a schematic diagram showing theconfiguration of a synchronous rectification type DC-DC converter. Theillustrated DC-DC converter 100 includes a high-side MOSFET 110, alow-side MOSFET 120, a Schottky barrier diode (SBD) 130, a coil 140, acapacitor 150, and a control IC 160. The DC-DC converter 100 iscontrolled by the control IC 160 so as to alternately supply current tothe high-side MOSFET 110 and the low-side MOSFET 120, to reduce thevoltage.

The conventional DC-DC converter 100 is made by mounting the foregoingfunctional devices on a printed circuit board, and then electricallyconnecting the electrodes of each functional device via wiring formed onthe printed circuit board.

The internal structure of the high-side MOSFET 110 may be made like aMOSFET described in patent document 1 below. In that case, the high-sideMOSFET 110 is configured as shown in FIG. 14. Specifically, thehigh-side MOSFET 110 includes a MOSFET chip 111, a frame 112, a gateterminal 110 a, a source terminal 110 b, and a drain terminal 110 c. Thegate electrode and the source electrode of the MOSFET chip 111 areconnected directly to the gate terminal 110 a and the source terminal110 b, respectively. The drain electrode is connected to the drainterminal 110 c through the frame 112. The low-side MOSFET 120 may beconfigured in a similar manner.

Patent Document 1: JP-A-2002-76195

As stated above, in the conventional DC-DC converter 100, the functionaldevices are electrically connected through the wiring formed on theprinted circuit board. Generally, the wiring formed on the printedcircuit board has certain wiring resistance and inductance. The wiringresistance is proportional to the length of the wiring, and inverselyproportional to the cross-sectional area thereof. The wiring inductanceis substantially proportional to the length of the wiring. Even if thehigh-side MOSFET 110 and the low-side MOSFET 120 are mounted adjacentlyon the printed circuit board, there is a limit to the reducible amountof the resistance and the inductance of the wiring between the sourceterminal 110 b of the high-side MOSFET 110 and the drain terminal 120 cof the low-side MOSFET 120.

The wiring resistance leads to an increase in power consumption of theDC-DC converter 100, and the wiring inductance leads to deterioration ofswitching performance of the DC-DC converter 100. In addition, thewiring inductance may cause electromagnetic interference (EMI).Specifically, the wiring inductance generates a magnetic field, and whenthe magnetic field fluctuates, noise is generated in the circuit. Suchnoise degrades the performance of the DC-DC converter 100.

Further, the frames 112, 122 provided inside the respective MOSFETs 110,120 also have the wiring resistance and the wiring inductance. Thismakes the foregoing issue more serious. In particular, when the DC-DCconverter 100 is used for high-frequency applications, the influence ofthe wiring inductance becomes greater.

DISCLOSURE OF THE INVENTION

The present invention has been proposed under the foregoingcircumstances. An object of the present invention is to provide a modulewith reduced wiring resistance and reduced wiring inductance.

To achieve the object, the present invention takes the followingtechnical measures.

The present invention provides a module comprising: a first functionaldevice including a base electrode, an emitter electrode and a collectorelectrode; a second functional device including at least one electrode;and a frame directly connected to both the electrode of the secondfunctional device and one of the base electrode, the emitter electrodeand the collector electrode. The frame includes a portion serving as aconnection terminal.

The above arrangement contributes to reducing the wing resistance andinductance between the functional devices, compared with an instancewhere the first functional device and the second functional device areconnected through an interconnection line formed on a printed circuitboard. Accordingly, a circuit including such a module can achieve lowerpower consumption and higher performance. In addition, the portion ofthe frame serving as the connection terminal can be used for making aconnection to another device on the circuit, which allows the user ahigher degree of freedom in designing the circuit.

In a preferred embodiment, the second functional device may include abase electrode, an emitter electrode, and a collector electrode.

Also in the above case, where the two functional devices are bothtransistors, it is possible to reduce the wiring resistance andinductance between the electrodes directly connected to the frame.

In a preferred embodiment, the first functional device and the secondfunctional device may be as arranged to face each other across theframe.

Such configuration minimizes the distance between the electrodesdirectly connected to the frame, thereby further reducing the wiringresistance and inductance.

Preferably, the collector electrode of the first functional device andthe emitter electrode of the second functional device are directlyconnected to the frame.

Such configuration enables reduction in wiring resistance and inductancebetween the collector electrode of the first functional device and theemitter electrode of the second functional device.

Other features and advantages of the present invention will become moreapparent through the following detailed description given with referenceto the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view showing a module according to a firstembodiment of the present invention;

FIG. 2 is a cross-sectional view taken along a line II-II in FIG. 1;

FIG. 3 is an exploded perspective view showing main portions of themodule according to the first embodiment;

FIG. 4 is a cross-sectional view of a module according to a secondembodiment of the present invention;

FIG. 5 is a perspective view showing a module according to a thirdembodiment of the present invention;

FIG. 6 is a cross-sectional view taken along a line VI-VI in FIG. 5;

FIG. 7 is an exploded perspective view showing main portions of themodule according to the third embodiment;

FIG. 8 is a perspective view showing a module according to a fourthembodiment of the present invention;

FIG. 9 is a cross-sectional view taken along a line IX-IX in FIG. 8;

FIG. 10 is an exploded perspective view showing main portions of themodule according to the fourth embodiment;

FIG. 11 is a circuit diagram of a step down DC-DC converter;

FIG. 12 is a circuit diagram of a drive circuit;

FIG. 13 is a circuit diagram of a synchronous rectification type DC-DCconverter; and

FIG. 14 is a cross-sectional view for explaining the structure of aconventional MOSFET.

BEST MODE FOR CARRYING OUT THE INVENTION

Embodiments of the present invention will be described below withreference to the accompanying drawings. FIGS. 1 to 3 illustrate a moduleaccording to a first embodiment of the present invention. The module ofthis embodiment corresponds to a single device into which the high-sideMOSFET 110 and the low-side MOSFET 120 shown in FIG. 13 are integrated.

The illustrated module 1 includes a high-side MOSFET chip 2, a low-sideMOSFET chip 3, conductive lead frames 4-8, and a resin package 9.

As shown in FIG. 3, the upper surface of the high-side MOSFET chip 2 isprovided with a gate electrode 2 a and a source electrode 2 b, and thelower surface of the chip is provided with a drain electrode 2. Asknown, a bipolar transistor has three electrodes called a baseelectrode, an emitter electrode, and a collector electrode. Theseelectrodes correspond to the gate electrode, the source electrode, andthe drain electrode of a MOSFET, respectively.

The gate electrode 2 a of the high-side MOSFET chip 2 is connected tothe frame 7, the source electrode 2 b to the frame 4, and the drainelectrode 2 c to the frame 6. Thus, the high-side MOSFET chip 2 isinterposed between the upper-side frames 4, 7 and the lower-side frame6.

The upper surface of the low-side MOSFET chip 3 is provided with a gateelectrode 3 a and a source electrode 3 b, and the lower surface of thechip is provided with a drain electrode 3 c.

The gate electrode 3 a of the low-side MOSFET chip 3 is connected to theframe 8, the source electrode 3 b to the frame 5, and the drainelectrode 3 c to the frame 4. Thus, the low-side MOSFET chip 3 isinterposed between the upper-side frames 5, 8 and the lower-side frames4, 7. The drain electrode 3 c of the low-side MOSFET chip 3 is solocated as not to be connected to the frame 7. The electrodes 2 a-2 c, 3a-3 c are attached to the corresponding frames 4-8 with solder orconductive paste, for example.

The frames 4-8 are made of metal such as copper, and electricallyconnected to the electrodes of the chips 2 and 3. As shown in FIG. 2,the frames 4, 5 are generally S-shaped in cross section, and one endportions of the respective frames serve as connection terminals of themodule 1. As shown in FIG. 3, the other end portions of the respectiveframes 4, 5 are L-shaped. The frames 7, 8 are also generally S-shaped incross section like the frames 4, 5, though not shown in FIG. 2, and oneend portions of the respective frames serve as connection terminals ofthe module 1. The frame 6 has a lower surface serving as a connectionterminal of the module 1.

As shown in FIG. 3, the lower surface of the other end portion of theframe 4 is connected to the source electrode 2 b of the high-side MOSFETchip 2. Also, the upper surface of the other end portion of the frame 4is connected to the drain electrode 3 c of the low-side MOSFET chip 3.Thus, the frame 4 is located such that the other end portion isinterposed between the upper surface of the high-side MOSFET chip 2 andthe lower surface of the low-side MOSFET chip 3.

The lower surface of the other end portion of the frame 5 is connectedto the source electrode 3 a of the low-side MOSFET chip 3. The uppersurface of the frame 6 is connected to the drain electrode 2 c of thehigh-side MOSFET chip 2. The lower surface of the other end portion ofthe frame 7 is connected to the gate electrode 2 a of the high-sideMOSFET chip 2. The lower surface of the other end portion of the frame 8is connected to the gate electrode 3 a of the low-side MOSFET chip 3.

As shown in FIG. 1, the lower surface of an end portion of the frame 4serves as an output terminal 4 a of the module 1. The lower surface ofan end portion of the frame 5 serves as a ground terminal 5 a of themodule 1. The lower surface of the frame 6 serves as an input terminal 6a of the module 1. The lower surface of an end portion of the frame 7serves as a control terminal 7 a of the high-side MOSFET chip 2 of themodule 1. The lower surface of an end portion of the frame 8 serves as acontrol terminal 8 a of the low-side MOSFET chip 3 of the module 1.

The resin package 9 encloses the chips 2-3 and the frames 4-8. The resinpackage 9 may be formed by molding. In this process, the chips 2-3 andthe frames 4-8 are disposed immovably at the predetermined positionsnoted above, and placed in a metal mold for forming the resin package 9.Then, a molten resin material for the resin package 9 is supplied tofill up the mold. By hardening the resin material, the resin package 9shown in FIGS. 1 and 2 can be obtained.

The operation of the module 1 will now be described.

The control terminal 7 a and the control terminal 8 a of the module 1receive a pulse signal from the control IC 160 (see FIG. 13). The pulsesignal inputted to the control terminal 8 a has inverted high and lowlevels with respect to the pulse signal inputted to the control terminal7 a. Accordingly, when a high level voltage is inputted to the controlterminal 7 a, a low level voltage is inputted to the control terminal 8a, and when a low level voltage is inputted to the control terminal 7 a,a high level voltage is inputted to the control terminal 8 a.

When the high level voltage is applied to the control terminal 7 a, thehigh-side MOSFET chip 2 is in electrical conduction state, while thelow-side MOSFET chip 3 is not. Hence, the current inputted to the inputterminal 6 a is outputted from the output terminal 4 a. The current thusoutputted charges magnetic energy in the coil 140 and electric energy inthe capacitor 150, and is outputted from the DC-DC converter 100.

When the low level voltage is applied to the control terminal 7 a, thelow-side MOSFET chip 3 is in electrical conduction state, while thehigh-side MOSFET chip 2 is not. Hence, the current inputted to the inputterminal 6 a is not outputted from the output terminal 4 a. In thiscase, the magnetic energy stored in the coil 140 and the electric energystored in the capacitor 150 are discharged and outputted from the DC-DCconverter 100.

In the DC-DC converter 100, the control IC 160 adjusts the duty ratio ofpulse signals inputted to the control terminals 7 a and 8 a (ratio ofthe high level duration to one period of the pulse signal), to outputthe required voltage.

Advantages of the module 1 will be described below.

In the embodiment above, the source electrode 2 b of the high-sideMOSFET chip 2 and the drain electrode 3 c of the low-side MOSFET chip 3are connected in a mutually facing manner across the frame 4.Accordingly, the length of the connection path between the electrodes 2b, 3 c is equal to the thickness of the frame 4, and the cross-sectionalarea of the connection path is equal to the area of the electrodes 2 b,3 c. Such configuration reduces the wiring resistance and inductancebetween the electrodes 2 b, 3 c.

Thus, by using the module 1, whose wiring resistance is reduced, it ispossible to reduce power consumption of the DC-DC converter 100 (FIG.13). Also, since the wiring inductance is reduced, the switchingperformance of the DC-DC converter 100 can be improved. Further, the EMIcan be suppressed, so that the DC-DC converter 100 can exhibit higherperformance.

Also, in the above embodiment, a portion of the frame 4 itself serves asthe output terminal 4 a. In this manner, a current from the connectionpoint between the source electrode 2 b of the high-side MOSFET chip 2and the drain electrode 3 c of the low-side MOSFET chip 3 can bedirectly outputted from the terminal. Thus, the module 1 can constitutethe DC-DC converter 100.

In the above embodiment, the module 1 is described as being used forproviding a synchronous rectification type DC-DC converter. It should benoted that the module 1 can enjoy the same advantages when applied toother circuits (for example, a power supply circuit or a motor drivecircuit). The structure of the module is not limited to that of theabove embodiment. Modules according to second through fifth embodimentswill be described below.

FIG. 4 depicts a module according to the second embodiment of thepresent invention. The module 1A according to this embodiment isdifferent from the module according to the first embodiment in thefollowing three aspects. First, a frame 5A is exposed at the uppersurface of the module 1A. Second, the drain electrode 2 c of thehigh-side MOSFET chip 2 is exposed at the lower surface of the module1A, so as to serve also as an input terminal. Third, a SBD chip 10(corresponding to the SBD130 in FIG. 13) is provided between the frame4A and the frame 5A. The SBD chip 10 has an upper surface and a lowersurface, provided with an anode electrode and a cathode electrode,respectively. In FIG. 4, the anode electrode of the SBD chip 10 isconnected to the lower surface of the frame 5A, and the cathodeelectrode to the upper surface of the frame 4A.

The second embodiment also enjoys the same advantages as the firstembodiment. Further, in the second embodiment, a heat dissipation plate(not shown) may be attached to the exposed surface of the frame 5A, soas to release heat efficiently. Also, since the frame 6 of the firstembodiment is not needed in the second embodiment, the production costcan be reduced. Further, the module 1A of the second embodiment includesthe MOSFET chip 2, 3 and the SBD chip 10 in a single package. Thus, thenumber of parts necessary for constituting the DC-DC converter 100 canbe reduced. In the module 1A, the chip located between the frame 4A andthe frame 5A may be another diode chip or a passive element such as aresistor, in place of the SBD chip. Also, the diode chip or the passiveelement chip may be located on the lower surface of the frame 4A, withan electrode of the chip connected to the frame 4A. In this instance,the other electrode of the chip may serve as a terminal exposed at thelower surface of the module 1A.

FIGS. 5-7 depict a module according to the third embodiment of thepresent invention. The module 1B of this embodiment is different fromthe module 1 of the first embodiment in that the high-side MOSFET chip 2and the low-side MOSFET chip 3 are located side by side on the uppersurface of the frame 4B, as shown in FIGS. 6 and 7. Also, since thechips 2, 3 are located side by side in the module 1B, the shape andlocation of the frames 4B-8B (see FIG. 7), as well as the shape andlocation of terminals 4Ba-8Ba provided on the lower surface of themodule 1B are different from those of the first embodiment.

In the third embodiment, the source electrode 2 b of the high-sideMOSFET chip 2 and the drain electrode 3 c of the low-side MOSFET chip 3are connected through a conductive path that is smaller in length andgreater in cross-sectional area than the conventional wiring formed on aprinted circuit board. Thus, the third embodiment can enjoy the sameadvantages as those of the first embodiment. Also, in the thirdembodiment, the module 1B can have a smaller thickness (the verticaldimension in FIG. 6) than the module 1 of the first embodiment.

In the foregoing embodiment, the source electrode 2 b of the high-sideMOSFET chip 2 and the drain electrode 3 c of the low-side MOSFET chip 3are connected, though the present invention is not limited to thisconfiguration. For example, the gate electrode of one MOSFET chip andthe source electrode of the other MOSFET chip can be connected, withreduced wiring resistance and inductance between the two electrodes.Thus, in this case again, the foregoing advantages can be enjoyed.

In the foregoing embodiments, the functional devices constituting themodules are MOSFET chips, though the present invention is not limited tothis. The same advantages can be enjoyed by using transistors other thanMOSFETs, or diodes, or passive elements such as resistors, or acombination thereof.

FIGS. 8 to 10 depict a module according to the fourth embodiment of thepresent invention. The module 1C of this embodiment differs from themodule 1 of the first embodiment (see FIGS. 2 and 3) in that a diodechip 11 is used in place of the low-side MOSFET chip 3 in the module 1.The diode chip 11 includes an anode electrode and a cathode electrodeprovided on two opposite surfaces, respectively. In FIG. 10, the anodeelectrode 11 a is arranged on the upper surface, and the cathodeelectrode 11 b is arranged on the lower surface. The module 1C alsodiffers from the module of the first embodiment in the shape of theframe 5C (see FIG. 10) and the shape of a terminal 5Ca (see FIG. 5)provided on the lower surface of the module 1C.

FIG. 11 is a circuit diagram of a step down DC-DC converter. The stepdown DC-DC converter 20 includes a MOSFET 21, a diode 22, a coil 23, acapacitor 24, and a control IC 25. In the step down DC-DC converter 20,the MOSFET 21 is brought into intermittent electrical conduction underthe control of the control IC 25, thereby lowering the inputted voltageto a predetermined level before the voltage is outputted.

By using the module 1C of the fourth embodiment for the MOSFET 21 andthe diode 22 of the step down DC-DC converter 20 shown in FIG. 11(indicated by dotted lines in FIG. 11), the wiring resistance andinductance between the source electrode of the MOSFET 21 and the cathodeelectrode of the diode 22 can be reduced. This enables reduction inpower consumption and improvement in performance of the step down DC-DCconverter 20.

A module according to the fifth embodiment of the present inventiondiffers from the module 1 of the first embodiment (see FIG. 2) in thatan NPN transistor and a PNP transistor are employed in place of thehigh-side MOSFET chip 2 and the low-side MOSFET chip 3, respectively.Drawings to illustrate the fifth embodiment are omitted since they wouldbe the same as FIGS. 1-3.

FIG. 12 is a circuit diagram of a drive circuit. A drive circuit 30includes an NPN transistor 31, a PNP transistor 32, capacitors 33, 34, agate resistance 35, a resistance 36, and a high-speed photocoupler 37.The drive circuit 30 provides, based on a signal inputted to thehigh-speed photocoupler 37, an amplified signal to the gate terminal ofan IGBT 40 serving as the switching element, and drives the IGBT 40.

Specifically, when the pulse signal inputted to the high-speedphotocoupler 37 is of a high level, the NPN transistor 31 is inelectrical conduction, so that a voltage +V_(GE) is applied to the gateterminal of the IGBT 40. On the other hand, when the pulse signalinputted to the high-speed photocoupler 37 is of a low level, the PNPtransistor 32 is in electrical conduction, so that a voltage is appliedto the gate terminal of the IGBT 40. In this manner, the signal inputtedto the high-speed photocoupler 37 is amplified and inputted to the gateterminal of the IGBT 40.

By using the module of the fifth embodiment for the NPN transistor 31and the PNP transistor 32 of the drive circuit 30 shown in FIG. 12(indicated by bold dotted lines in FIG. 12), the wiring resistance andinductance between the emitter electrode of the NPN transistor 31 andthe emitter electrode of the PNP transistor 32 can be reduced. Thisenables reduction in power consumption and improvement in performance ofthe drive circuit 30.

1. A module comprising: a first functional device including a baseelectrode, an emitter electrode and a collector electrode; a secondfunctional device including at least one electrode; and a frame directlyconnected to both the electrode of the second functional device and oneof the base electrode, the emitter electrode and the collectorelectrode, the frame including a portion serving as a connectionterminal.
 2. The module according to claim 1, wherein the secondfunctional device includes a base electrode, an emitter electrode and acollector electrode.
 3. The module according to claim 1, wherein thefirst functional device and the second functional device are arranged toface each other across the frame.
 4. The module according to claim 2,wherein the collector electrode of the first functional device and theemitter electrode of the second functional device are directly connectedto the frame.